1. Field of the invention
The present invention relates to a phase change optical information recording medium.
2. Description of the prior art
There are known optical information recording media such as a magneto-optical disk, a phase change optical disk, etc. which have been developed as rewritable recording media of an EDRAW (Erasable Direct Read After Write) type.
In such the recording media of phase change type, there is an optical disk having a recording thin film made of a chalcogenide alloy, for example. The information to be recorded into such a phase change optical disk is written by the irradiation of laser beam, and then the recorded information is read by detecting the difference of reflection due to the phase change between crystalline and amorphous states in the recording layer. The laser beam is used with its intensity modulated in the writing, erasing and reading (overwriting) modes. For example, a plurality of minute amorphous domains are provided along tracks of the recording film whose surface is a coarse crystalline state by heating and quick cooling due to irradiated spots of scanning laser beam. In this way, the information is recorded as rows of amorphous domains on the tracks of the optical disk.
FIG. 1 is a schematic illustration of data waveform which is reproduced from a phase change optical disk after the overwriting has been repeatedly performed thereon, the phase change optical disk being formatted with a sampled servo tracking method. In case that this sampled servo tracking method is based on ISO standards, any information is not recorded on the predetermined channel in a unit byte consisting of a plurality of channels, for example 15 channels. Therefore, no amorphous domain is formed at the corresponding portion to the predetermined channel, for example the 15th channel, in the pre-pit region along the track of the recording film. The reproduced data waveform is therefore distorted from the portion (A) of the predetermined channel through the following data region, as shown in FIG. 1, and this distortion causes data error in the reproduction of the recorded information.
FIG. 2 is a schematic illustration of data waveform which is reproduced from a phase change optical disk after the over-writing has been repeatedly performed thereon, the phase change optical disk having grooves on both sides of the recording track thereof and formatted with continuous servo tracking method. The data error is also distorted at the rear terminal portion (B) of the data region from far the pre-pit region, as shown in FIG. 2, when the data reproduced through the continuous servo tracking method on the phase change optical disk.
In this way, in this phase change optical disk, there is a problem that the overwriting characteristic deteriorates when the overwriting is repeatedly performed.